Seal for hard glass



Patent ed Nov. 13, 1928.

PATENT orrlca.

UNITED STATES WILLIAM-BENJAMIN GEBO, OF BLOOMFIEIiD, NEW JERSEY,ASSIGNOR IO WESTING- HOUSE LAMP COMPANY, A CORPORATION OF PENNSYLVANIA.

am ton 1mm: GLASS.

mi Drawing.

The present invention relates to ,a novel metallic sealv for evacuatedcontainers composed of hard glass, and it involves the use of an alloyof tungsten and molybdenum.

5 It has been proposed to employ molybdenum or tungsten as seals forevacuated containers consisting of hard or silica glass. I havediscovered that an alloy of these metals in suitable proportion may beemployed for this pur ose. i

There ore, it is an object of my invention to provide a suitable s'ealfor hard glass which combines certain of the advantages obtained byusinu mol bdenum or tungsten separately.

Anot er 0 ject of the invention is to provide a seal for hard-glasswhich may be read- "ily Varied with respect to its coeflicient of expansion so as to make the same suitable for a great variety of glasseshaving different coefiicie'nts of expansion.

Other objects of the invention will become apparentas the followingdescription is read. 7 Tungsten and molybdenum have been used quiteextensively for sealing to. glass, especially silicate glasses. Inmanufacturing a tungsten seal it is customary to bead the metal severaltimes if a straight-through seal is made, but in press work the secondbeading operation is not always essential. Beading 0 comprises slippinga glass tube over the metal wire and heating the glass and metal untilthe glass is fused to the metal. In making seals employing molybdenum ithas been found preferable to employ the wrapping method 85 whichconsists in heating the molybdenum wireand applying thereto molten glassobtained from a cane or solid rod of glass.

Molypdenum seals are found more desirable if a straight-through sealisto be employed,

whereas for press work the tungsten seal is better suited. i

It is further evident that either molybdenum or tungsten alone (does notfurnish any wide range of expansion coeflicients whereas by merelyaltering the: proportions of the constituents of an alloy of tungstenand molybdenum a considerable range may be obtained which makes thealloy suitable for a variety of hard glasses having differentooefficients of expansion. Tungsten has a coefficient of expansion from0 C. to about 500 C. of from 4.2 X 10' to 4.8 X 10 respectively, andcommercial molybdenum between Application al a min,

'1926. Serial No. 125,591.

251 and 100 C. from 4.6 X 10"" to 5.4- X 10' per degree centigrade,respectively, as determmed by the ureau of Standards.

Although it has been proposed to employ as a seal an alloy of iron andnickel, the composition of which can be varied to obtain differentcoefficients of expansion, such material alone is unsuitable for sealingpurposes since it does not wet the-glass and form an hermetic seal.Therefore, it is customary in using such an alloy in seals to combinetherewith as a coating material a substance such as copper or platinumwhich w'ets the glass and seals thereto.

I have found that an alloy of tungsten and molybdenum possesses all ofthe desirable properties essential to the formation of an hermetic sealand at the same time provides for obtaining a wide range of coefficientsof expansion suitable for a number of different glasses having differentcoefficients of expansion.

A specific embodiment of the invention may comprise about 80% oftungsten and about 20% of molybdenum, although as indicated above, theseproportions may be varied to suit special needs. If a Wire having a highcoeflicient of expansion is desired, the proportion of tungsten shouldbe increased and vice versa if a lower coeflicient of expansion isdesired. Tungsten has a lower coefiicient of expansion than molybdenum,therefore the greater percentage of tungsten employed the. closer thecoeflicient of expansion of the alloy is .to tungsten.

The specific alloy composition stated has been found to satisfactorilyseal to a hard glass known as G 7 02P, such glass consisting of about72% of silica (SiO 15% of boron oxide (B 0 6.5% of lead oxide (PbO)about 4.4% of sodium oxide (Na O) and about 2% of aluminum oxide (A1 0This glass has a melting point of about 760 C. and a coefiici'ent ofexpansion of about 41.5 X 10-.

The alloy may be prepared by mixing suitable proportions of the oxidesof tungsten and molybdenum and reducing to metal by means of hydrogen inaccordancewith standard processes employed in the manufacture oftungsten. The metal powders may be employed directly without goingthrough the reduction step. The powders of the metal may then beagglomerated by pressing in suitable molds and subjecting the pressedpowders to heat treatment in hydrogen gas until they are sufficientlystrong to permit handling. The sintered bars are then rendered dense andcoherent by passage of an electric current therethrough, this latteroperation being termed the treating step. The treated bar may then bemechanically worked to wire or filamentary sizes by hot-swaging anddrawing, slightly lower temperatures than those employed for workingtungsten being preferably employed. The entire process of sintering,treating and mechanical working is substantially like that employed inmanufacturing tungsten with the exception that such modifications areresorted to as found essential because of the character of materialundergoing treatment.

An alloy of tungsten thus formed may be employed as a leading-in wirefor lamps, radio tubes, rectifiers and the like or may be utilizedwherever it is desired to make an hermetic seal to hard glasses.

Modifications of the invention may occur to those skilled in the art,however, such modifications are contemplated by me as come within thescope of the invention as defined in the appended claims.

What is claimed is:

1. In combination with a container consisting of hard glass, a conductorsealed therein and consisting of an alloy'of tungsten and molybdenum.

2. The combination with a container con sisting of a glass having acoefiicient of expansion of a out 4.5 X 10", of a conductor sealedthereto consisting of an alloy of tungsten and molybdenum.

3. The combination with a container consisting of a glass having acoeflicient of expansion of about 4.5 X 10-, of a conductor sealedthereto consisting of an alloy of tungsten and molybdenum in theproportion of about 80% and about 20%, respectively.

4. An electric appliance of the character described provided with aleading-in conductor composed of an alloy of tungsten and molybdenumsealed in hard glass.

In testimony whereof, I have hereunto subscribed my name this 27th dayof July, 1926.

WILLIAM BENJAMIN GERO.

